Generally speaking, seat belt retractors serve the purpose of winding up a seat belt of the seat belt device in motor vehicles. Typically the seat belt retractor has, among other things, a blocking device which is actuated subject to the exceedance of predetermined acceleration values of vehicle deceleration and may further sense seat belt withdrawal acceleration and in this way subsequently blocks the seat belt against further seat belt withdrawal movement. A sensor device is provided to actuate the blocking device subject to the exceedance of a predetermined value of vehicle deceleration (vehicle-sensitive sensor device), which sensor device typically includes an inertial mass, supported on a sensor surface and abutting on a blocking lever. Furthermore, a control disk is provided with a toothing (gear teeth), which control disk is rotatably supported on a belt shaft of the seat belt retractor, and which, with relative movement with respect to the belt shaft, forces a locking catch of the blocking device to perform a movement that steers the catch into a blocking toothing. The movement of the control disk relative to the belt shaft is caused by the sensor device by the inertial mass being deflected, and the blocking lever thereby being deflected. The deflection of the blocking lever causes it to engage into a toothing of the control disk, so that the control disk is stopped with respect to the belt shaft.
However, for various reasons it has proved useful to deactivate the vehicle-sensitive sensor device starting at a certain belt withdrawal length. This can, for example, be the case when there is switching between an ELR (emergency locking retractor) and an ALR (automatic locking retractor) operation of the seat belt retractor, or in seat belt retractors that are installed in tiltable backrests, if the belt shaft should always be blocked at certain lengths of seat belt withdrawal, or if a blocking of the belt shaft should not take place starting at a certain seat belt retraction length even when there is a deflection of the inertial mass.
In this respect it is known, for example from EP 2 282 916 B1, to fix the blocking lever of the vehicle-sensitive sensor device with a second blocking lever whose movement is controlled by a counter gear driven by the belt shaft. Here the counter gear is formed by a gearing with a gearwheel disposed on a rocker, wherein the rocker, due to a certain arrangement of skips in the toothing of the gearwheels is forced, at a predetermined length of belt extraction, to perform a rocking movement by which the movement of the second blocking lever is controlled.
The object of the present invention is to provide a seat belt retractor with which the switching-on and switching-off of the sensor device that detects the vehicle deceleration is provided in a simple manner achieved by a seat belt retractor described herein and illustrated by the accompanying figures.